Field of the Invention
The present invention relates to a thin fan, and more particularly, to a thin fan having a high structural strength and a low motor resonance noise.
Descriptions of the Related Art
With the advancement of science and technologies and the rapid development of manufacturing processes, many consumer electronic products have evolved towards good portability and a light weight to meet the demands of modern consumers. Therefore, along with portable products such as notebook computers, mobile phones and MP3 players, electronic products that conventionally have a bulky volume and poor portability such as projectors and head-mounted displays (HMDs) have also appeared in the market with a lighter and thinner form.
To meet the demands for portable and lightweight products, various kinds of parts and components used in such products must be miniaturized correspondingly to be installed therein. Although these parts and components are further reduced in volume, their performance shall not be compromised but shall be subjected to stricter requirements. A concern is that with insufficient inner space and poor heat dissipating efficiency, the thermolysis of the parts and components is significantly affected, thereby, affecting the performance of these products and also shortening the service life of the products.
Therefore, the practice of disposing a thin fan to actively dissipate the heat has been gradually adopted in the art. However, general centrifugal fans that are currently widely used in notebook computers have an overall height that ranges from about 8 millimeters (mm) to 10 mm, so they have become inapplicable to thin electronic products such as tablet personal computers (PCs), smart mobile phones or ultrathin notebook computers, which are often made to have a thickness less than 9 mm. In consideration of the thickness of the housing and preserved gap for air intake, the overall height of a fan for such a thin electronic product must be made to be less than 4 mm so that the fan can be installed and used successfully in the electronic product. However, making such a thin fan is difficult in the design of moulds, selection of materials, manufacturing, assembling and arrangement of parts.
For example, the joining surface between a shaft and an impeller is reduced because of the reduced height of the fan. To have a firmly joined the shaft and the impeller, a conventional thin fan as disclosed in Taiwan Patent Application No. 94140896 has a shaft and an impeller joined by an assembling element. However, the use of additional assembling elements increases the cost and the overall height of the fan because the assembling element extends above the impeller. In addition, this structure is formed by a plate through punching and bending and if the blades can only extend in a direction towards the annular plate, the height of the blades is limited. As a result, the heat dissipating effect of the air flow driven by the rotating blades is also quite limited.
In another example, a thin fan as disclosed in Taiwan Patent Application No. 94140897 has a shaft joined through an assembling hole formed in both the impeller and the sheet magnet. However, the sheet magnet of this structure extends above the tubular shaft, so the height of the tubular shaft will be reduced because of the sheet magnet. The reduced height of the tubular shaft makes it necessary to use a short bearing. Since the bearing contains a reduced amount of lubricant, the lubricant tends to dry off. This may cause direct friction between the shaft and the bearing and significantly reduce the service life of the bearing.
As a further example, a thin fan as disclosed in Taiwan Patent No. 1299771 has a shaft joined through a spindle seat. However, the spindle seat, which is disposed above a tubular shaft, also reduces the height of the tubular shaft. Consequently, the bearing contains a reduced amount of lubricant, so it has a shortened service life. Moreover, the blades of this structure can only be disposed in the periphery of the spindle seat and above a magnet, so the height of the blades is limited, which affects the heat dissipating effect.